The Forearm
The forearm is one of the more confounding areas of the body. Most of the muscles that move the hand are on the forearm, and for every motion of the palm and fingers there is a corresponding muscle to execute it.
In order to simplify the forearm, we can break it into four masses. The first mass is brachioradialis (bray-kee-oh-ray-dee-AL-iss). This large muscle is the only flexor that attaches to the lateral epicondyle of the humerus; the rest go to the medial epicondyle. This fact, plus its size, make it a handy divider between the extensor and flexor masses described below.
The flexor mass includes the rest of the muscles that curl the wrist and fingers into a closed position. All of these muscles originate on the medial condyle of the humerus. Most of them lie on the palm-side of the forearm. (An important influence on their form by biceps is described under the listing for that muscle.)
The extensor mass includes muscles that straighten the wrist and fingers and pull them into an open position. All of these muscles orginate on the lateral epicondyle of the humerus, and mostly lie on the dorsal side of the forearm.
The fourth division is the thumb group of the forearm. These two muscles on the forearm move the thumb. They originate lower down on the radius and ulna.
Just as brachioradialis divides the the flexor and extensor masses in front, the ulna divides them in the back. The lower end of the ulna and the elbow are readily visible, and it is easy to imagine the line between them that divides the two groups.
Every forearm muscle can be distinguished only on the most heroic kind of figure. More commonly, the forearm can be drawn simply in terms of the four masses, especially when the arm is relaxed. These masses provide a useful starting point for further development of the shapes of the arm.
To avoid tiresome repetition, the following pronunciations and derivations are given here:
| carpi | CARP-ee | referring to the carpal or metacarpal bones |
| digitorum | dij-ih-TOE-rum | digits - the fingers |
| pollicis | POL-iss-iss | the thumb |
| radialis | ray-dee-AL-iss | the radius or radial side of arm |
| ulnaris | ul-NAIR-riss | the ulna or ulnar side of arm |
Extensor, flexor, longus, and brevis are used as above. This makes most of the names of the forearm muscles self-explanatory.